import { Observable } from 'rxjs/Observable'
import { of } from 'rxjs/observable/of'
import { map } from 'rxjs/operator/map'
let numbers = Observable.of(1, 2, 3);
let letters = Observable.of('a', 'b', 'c');
let interval = Observable.interval(1000);
let result = numbers.concat(letters).concat(interval);
result.subscribe(x => console.log(x));
